1. Field of the Invention
The present invention relates to caster wheels and, more particularly, to a brake for caster wheels and, most particularly, to a wheel lift and brake assembly for caster wheels. The description herein is focused on application to wheelchairs, but the invention is applicable to shopping carts, material transport containers, health or other disability-related appliances, and other applications utilizing caster wheels to improve maneuverability.
2. Background Information
Wheel chairs are widely used to contribute to the mobility of persons for whom normal walking is not practical. A number of variations have been made, including various powered and manually propelled devices. Many users of manually powered wheelchairs find it easy to maneuver on flat, hard floors, but have difficulty negotiating over even small obstacles. In wheelchairs, the weight of the user is generally borne on four wheels; the two larger diameter rear drive wheels, and the two smaller caster wheels, typically located in the front. Chair motion is controlled by muscle power applied by grasping the propulsion handrails, thereby inducing forward, reverse, or turning wheelchair motions. The large drive wheels are intended to carry much of the load, while the smaller diameter casters provide sufficient support such that the user is unlikely to tip over forward or backward. Overall structural support is provided by the tubular chair frame.
Casters enable 360-degree rotation of each caster wheel about its vertical spin axis, so that in the absence of obstacles and while operating on level surfaces, the direction taken by the wheelchair is controlled solely by the relative forces applied to the drive wheels by the hand rails. Under ideal conditions, such a wheelchair is extremely maneuverable, since the combination of two front caster wheels and two independently driven rear wheels provide motion in any direction.
However, if an obstacle such as a door threshold or elevation change in an otherwise smooth, level surface is encountered, the situation is more complicated, and the above suspension system is more difficult to use. The navigation problem is composed of two parts: (1) While all wheels require some force to overcome obstacles, small diameter wheels require larger forces to overcome obstacles. The caster wheels typically have much smaller diameters than the larger drive wheels, so as to enable a more compact footprint for the wheelchair, and to permit unfettered turning ability. However, the smaller the castor wheel diameter, the greater the difficulty in overcoming even small obstacles. (2) If an obstacle is disposed such that the caster encounters the obstacle in an oblique or off-center manner, the caster wheel may be forced to turn in an undesired direction, making navigation very difficult or impossible. Both problems are addressed by the current invention: Normal manual wheelchairs are difficult to maneuver over even small obstacles, both for when the obstacle is encountered head on, or even more seriously, obliquely!
The present invention centers on several improvements in the design of manually propelled wheelchairs that are intended to improve their ability to overcome obstacles, such as door thresholds, small changes in elevation, or other deviations from a flat floor. The inventor proposes simple modifications in the design of manual wheelchairs. The three proposed modifications are similar, in that means are provided such that as an obstacle is encountered, the obstacle is detected, and a castor spin axis brake is activated so as to resist caster rotation in the early phase of the encounter. As the obstacle is further encountered, the load is transferred to the caster wheel, the spin axis brake is automatically released, and the mechanism is returned to the starting condition. These three means are designated as “Wheelaids.” “Wheelaids” are incorporated into caster wheels. Wheelaids significantly reduce the forces necessary to surmount obstacles without materially changing the maneuverability or ease of operation of wheelchairs so equipped, and add only a little weight. Wheelaids are not intended to allow wheelchairs to negotiate curbs, stairs, or other similar obstacles. Wheelaids can also be applied to powered wheelchairs, potentially resulting in lower motor torque requirements, lighter designs, or longer cruising ranges. Three variations of wheelaids are described below. The first variation utilizes what is called a Wheelcrutch, the second variation utilizes a Secondary Raised Wheel, and the third utilizes what is called a Wheelramp. In the following discussion, the description, “larger” or “smaller,” wheel refers to the wheel diameter, not the wheel or tread width.